Hatem M. Seliem

Bond Characteristics of ASTM A1035 Steel Reinforcing Bars

This paper presents results from a study of the bond characteristics of high-strength steel reinforcing bars that conform to ASTM A1035. In the study, a total of 69 large-scale beam-splice specimens were independently tested at 3 universities. Concrete with nominal strengths of 5000 and 8000 psi (35 and 55 MPa) were used. Maximum bar stresses were compared with predictions obtained using the bond equations in the ACI 318-05 code provisions and those proposed by ACI Committee 408. Maximum stress levels of 120, 110, and 96 ksi (830, 760, and 660 MPa) were developed in No. 5, No. 8, and No. 11 (No. 16, No. 25, and No. 36) bars, respectively, not confined by transverse reinforcement. The failure of beams with spliced bars not confined by transverse reinforcement was sudden and produced explosive spalling of the concrete cover over the entire splice length. Providing confinement for No. 8 and No. 11 (No. 25 and No. 36) spliced bars using transverse reinforcement allowed stresses of up to 150 ksi (1035 MPa) to be developed. The design equations in ACI 318 showed a large percentage of the developed/calculated strength ratios below 1.0, indicating they should not be used in their present form for development and splice design with high-strength reinforcing steel The ACI Committee 408 equation is more conservative and provides a reasonable estimate of the strength for both unconfined and confined splices using a strength reduction factor of 0.82 and design parameters (cover, spacing, and concrete strengths) similar to those used in this study.

Shear Behavior of Large Concrete Beams Reinforced with High-Strength Steel

This study seeks to quantify the benefits of using high-strength steel for concrete reinforcement and provides experimental evidence of its high strength capabilities. Test results are presented of six large-size concrete beams reinforced with either conventional- or high-strength steel and tested up to failure. The beams were constructed without web reinforcement to evaluate the nominal shear strength provided by the concrete. The shear behavior, ultimate load-carrying capacity, and mode of failure are presented. The applicability of the current ACI design code to large-size concrete beams constructed without web reinforcement is discussed. The influence of the shear span-depth ratio, concrete compressive strength, as well as the type and the amount of longitudinal steel reinforcement is investigated. Findings indicate that using high-strength steel alters the mode of failure from diagonal tension to shear compression failure and results in higher shear strength compared with using conventional steel. Findings also suggest that the current ACI shear design provisions are unconservative for large-size concrete beams without web reinforcement. The expression needs to account for the size effect and reinforcement characteristics.

Development Length of Unconfined Conventional and High-Strength Steel Reinforcing Bars

The development length equation specified by ACI 318-08 and the similar equation recommended by ACI 408R-03 are based on extensive test results using conventional reinforcement conforming to ASTM A615/A615M and A706/A706M. With the development of new ASTM A1035/A1035M high-strength steel reinforcement, several studies have been conducted to examine whether the current equations are applicable for the new high-strength reinforcing steel. These studies have shown that the current equations could, in some cases, overestimate the bond strength of high-strength steel bars. This paper proposes a new equation for the bond strength of unconfined reinforcing bars for all three types of steel. The proposed equation for high-strength steel is compared to extensive test data reported in the literature and is found to be more accurate than ACI 318-08 and ACI408R-03 equations specified for conventional reinforcement.

Behavior of Concrete Piles Confined with CFRP Grid

Synopsis: This paper describes an experimental program undertaken to study the behavior and effectiveness of using Carbon Fiber Reinforced Polymer(CFRP)Grid, as an alternative for steel spirals to confine precast concrete piles. The research focuses on the effectiveness of the confinement of the specified C-Grid on the concrete core of piles. The experimental program consists of a total of seven short piles including one without confinement, two with steel spiral and four with C-Grid. The parameters included in the study were the number of grid layers, the overlap length, and the spacing between the circumferential wires of C-Grid. All the specimens were subjected to concentric axial compression up to failure. Results indicate that the specified C-Grid can provide equivalent performance or more than typical spiral steel reinforcement for precast prestressed concrete piles. The paper also presents an analytical model to predict the performance of piles reinforced with C-Grid as spiral reinforcement. The analytical model yields results that match well with the experimental results.

Behavior of Concrete Bridge Decks Reinforced with MMFX Steel

Corrosion of steel reinforcement is considered to be one of the leading causes of deterioration of concrete bridges. This fact has led to the development of numerous technologies such as corrosionresistant steel that attempt to mitigate this expensive problem. The recent development of highstrength, high corrosion-resistant steel, commercially known as Micro-composite Multi-Structural Formable (MMFX) steel, is a promising technology. MMFX steel offers its high corrosion resistance without the use of the coating technologies. This characteristic was achieved by proprietary alteration of the steel composition and microstructure. In addition, the control of MMFX steel’s morphology of its microstructure has resulted in its higher strength. Use of MMFX steel could lead to potential savings through using less reinforcement ratios due to its higher strength characteristics and longer service life of structures because of its high corrosion resistance. Recently, many state transportation departments have begun to use MMFX steel as a direct replacement for regular Grade 60 steel in concrete bridge decks. However, despite these field applications, there is insufficient information about the behavior of such concrete bridge decks utilizing MMFX steel as main reinforcement. This paper evaluates the use of MMFX steel as main flexural reinforcement in concrete bridge decks in light of test results. Assessment of the effect of the arching action on the strength of bridge decks due to the use of this new steel is also presented.

Assessment of vehicular live load and load factors for design of short-span bridges according to the new Egyptian Code

Abstract The new Egyptian Code (ECP-201:2012) introduces new vehicular live loads (VLL) and new load combinations for the design of roadway bridges. The new VLL and load combinations introduced in ECP-201:2012 are fundamentally different than those presented in previous versions of the code. The impact of these new loads and load combinations on the design of new bridges or the structural safety of the existing bridges that have been designed according to ECP-201:2003 or ECP-201:1993 has not been fully addressed for the different bridge deck systems. Three different bridge deck systems, i.e. concrete I-shaped girders, composite steel plate girders, and concrete box-girders with different spans were numerically modeled using two-dimensional grillage analogy. The bridge decks were analyzed under main gravity loads using VLL according to ECP-201:2012 and ECP-201:2003. The internal forces of individual load cases, total un-factored load combination, and total factored load combination of ECP-201:2012 and ECP-201:2003 were compared. The study shows that concrete box-girders designed according to ECP-201:2012 and ECP-201:2003 using the ultimate limit state method yield almost the same demand. Despite the increase in the VLL of ECP-201:2012, and consequently the live load forces, concrete I-shaped girder bridges will be subjected to less total factored internal forces in comparison to ECP-201:2003 This is attributed to the interaction between the live to dead loads ratio and the load combinations. Design of composite steel plate girder bridges according to ECP-201:2012 using the allowable stress design method yields over designed sections.

Confinement of Concrete Piles with FRP

Precast piles are typically reinforced with steel spiral to provide confinement for the concrete core to increase the load carrying capacity as well as ductility of the pile. Confinement is particularly critical within the top region of the pile to resist the impact forces during driving. Due to direct exposure of piles to soils and harsh minerals, corrosion of outer spiral can compromise the long-term durability of typical piles. Since carbon fiber reinforced polymer (CFRP) materials are non-corrosive, they provide a promising alternative to the spiral steel for precast piles. This paper summarizes test results of an experimental program undertaken to evaluate the performance of specially designed CFRP Grid to replace the steel spirals for piles. Seven short columns, representing a 914 mm long section at the top of a pile were tested up to failure to study the effectiveness of the proposed CFRP Grid as reinforcement for confinement.